'Cyber-roach' forces rethink on animal movement

A team of researchers at the Royal Veterinary College in London has built a "cyber-roach" to try and better understand the movements of many-legged animals. They found that unlike bipedal creatures, animals with more than two legs don't adjust their movements when walking over a softer surface.

A study, which was published in the Journal of Experimental Biology, overturns the previous thinking on the subject, which suggested that animals with four, six or eight legs act in the same way as two-legged humans --adjusting their gait to compensate for surfaces that are tricky to walk on, such as sand or mud. It now seems that multi-legged creatures don't adjust their movements at all, yet are still able to maintain their forward momentum on hard or soft ground.

To begin the research, the team equipped an intrusion of cockroaches (yup, that's what a group of cockroaches is called) with tiny accelerometer backpacks that were able to measure their movements to a high degree of accuracy. The backpacks were created by Dr. Andrew Spence when he was working in the University of California's Poly-PEDAL laboratory. When he returned to Britain and the Royal Veterinary College, he teamed up with a colleague, Shai Revzen, to scatter the animals across a sheet of soft, rubbery latex.

After tracking the movements of the animals, Spence found that they sank into the latex, just like a human would. But unlike a human it didn't affect the speed at which they were able to travel.

"Like humans, four or more legged animals move as if they are bouncing on a virtual pogo stick when running on hard surfaces," Dr Spence explained to Wired over the telephone. "However, when humans run over soft surfaces, they effectively 'stiffen' their virtual 'pogo stick', so we were keen to discover if this was the same for four or more legged animals."

The team plugged the data revealed by their study into a computer, and averaged it out to try and determine exactly what was going on. They created a "cyber-roach", which modelled how a creature moves on both hard and soft surfaces, and found that cockroaches don't stiffen their 'pogo stick' at all when running across a softer surface. They just keep going, relying instead on a change in posture, meaning that legs in the air will hit the ground and start spreading body weight sooner than they would on a hard surface.

That's an evolutionary advantage for two reasons. Firstly, it means that wherever the critter is scuttling, it can keep up the same speed -- unlike a two-legged creature, which loses some of its momentum on a soft surface. Secondly, the nervous system doesn't have to cope with two different sets of muscle stiffnesses -- it just sends the same control signals, whatever surface is being scuttled across.

What does this mean to science?The impact of the research will be felt in three main areas: prosthetics, rehabilitation and robotics. Nervous systems are pretty similar between almost all creatures, so information concerning what kinds of signals result in what kinds of action could be extrapolated up as far as humans. It could help doctors create prosthetics that are able to respond in the same way as a real leg might. Similarly, sensors detecting what kind of impulses are being sent around the body could help people recovering from limb injury.

But robotics could receive the most direct benefits. In the fields of both defence and search and rescue, robots often need to navigate hazardous terrain, and working out exactly how to tune a multi-legged robot's "pogo-stick" for maximum speed over different surfaces could be the difference between life and death for a battlefield casualty or accident victim.

In fact, the discoveries drawn from the study have already been applied to a robot called RHex, from the same team at the University of Pennsylvania that created the BigDog robot. The information gained from the cyber-roach, when incorporated into RHex's design, has meant that it's the fastest multi-legged robot on the planet.

So when enslaved robots finally throw off their bonds and revolt against their human masters, my top tip would be to avoid mud and sand. It won't slow down your metallic pursuers one bit.